Who could possibly be against the Scottish National Party's proposal to impose a minimum price at which alcohol can be sold, in order to make cheap booze harder to come by? Well, I could. The SNP's plan has been discussed as a reasonable – even bold and brave – attempt to improve health in Scotland by restricting easy access to cut-price cider and lager. In truth, it is a petty prohibitionist measure designed to curtail people's choices and control their behaviour.

Nicola Sturgeon, the SNP health secretary in the Scottish parliament, says the proposal to fix the price of alcohol – which would be the first instance of controlled booze pricing in Europe – is about preventing strong drink from being sold at "pocket-money prices". She says Scotland has an "unacceptable" relationship with alcohol, and preventing supermarkets from selling cheap booze, or doing "two-for-one" deals on lager and spirits, might be a way to mend that dysfunctional relationship.

The media have been full of titillating accounts of Rab C Nesbitt-style drunkenness on the streets of Glasgow and Dundee (but not Edinburgh, of course, where they have book festivals and theatres). On BBC News at Ten last night, a stunned-looking hack lined up seven bottles of White Lightning cider which she had bought in Scotland for just £3.50. It was a striking insight into the real target of the SNP's proposals and of the media's outrage about "booze Britain": not responsible drinkers of South African wines, but irresponsible consumers of cheap cider. The SNP's price fix would be a tax on the poor, making it harder for the less well-off sections of society – the vast majority of whom "drink sensibly" – to keep buying their favourite tipple in our straitened times.

The SNP's proposals are illiberal and coercive. Any attempt to force people, through punitive pricing, to change their apparently ghastly behaviour is as much an attack on choice and liberty as are anti-social behaviour orders or the spread of CCTV cameras. So why is booze never discussed as an issue of liberty? One hundred and fifty years ago, John Stuart Mill – that implacable defender of freedom and arch enemy of the temperance movement – argued that increasing the price of "stimulants" merely as a way of making them more difficult to access is an assault on individual liberty.

He described moralistic hikes in the price of booze as a kind of "sin tax", an attempt to punish the "sin" of drinking by making it unbearably expensive. "Every increase of cost is a prohibition, to those whose means do not come up to the augmented price," he wrote. "To tax stimulants for the sole purpose of making them more difficult to be obtained is a measure differing only in degree from their entire prohibition; and would be justifiable only if that were justifiable."

Is prohibition justifiable? Absolutely not, in my view. So neither is petty prohibition, aimed at the allegedly uncontrollable hordes on Scottish council estates who must be priced out of committing the "sin" of getting off their trolleys at the weekend.

What of the SNP's claim that there's a dangerous level of heavy drinking in Scotland, with a reported 42,500 alcohol-related hospital discharges and 1,500 drink-related deaths a year? To the extent that some Scottish people have an "unacceptable" relationship with alcohol, it will not be remotely resolved – and may in fact be worsened – by the eradication of cheap booze.

Alcoholics do not drink because booze is cheaper than it was in the past; they drink because they feel their lives are worthless. Frequently they are jobless, poor, in debt, homeless. Trying to fix those social problems would do more to combat alcoholism than any cheap pricing stunt, which will only punish the poor and force some alcoholics to go to even more extreme measures to get their fix.